1. Field of the Invention
The present invention relates to a vehicle environment monitoring system that monitors an external environment of a vehicle on which the system is installed. The system detects an external object, which may collide with the vehicle from an image obtained by an imaging device mounted on the vehicle. The system hereof assists a user in avoiding a potential collision against a large animal, such as a deer, a bear or the like, since such collision has an adverse influence on the vehicle.
2. Description of the Prior Art
Conventionally, a warning device for giving a warning when the distance between the vehicle and an object approaching the vehicle becomes short was proposed by Japanese Laid-Open Patent Publication No. 2001-6096. The device detects a distance between the vehicle and the object based on the displacement between images of the object, that is, the parallax of images obtained by two cameras mounted on the vehicle. According to this device, the change rate of the detected distance is calculated as a relative speed, and a time period TY until the estimated time the vehicle may collide with the object (an estimated allowance time period TY) is calculated based on the relative speed and the distance. Further, a warning is given when the estimated allowance time period TY is shorter than a predetermined allowance time period T.
FIG. 22 is a diagram showing actually detected data of an error of the relative speed detected by the method shown in the above publication. As is clear from FIG. 22, the error of the detected relative speed increases as the distance from the object increases. Therefore, calculating the estimated allowance time period TY based on the relative speed and the distance raises a problem that the warning may be given too early or too late.
For example, if the detected relative speed is 60 km/h at a distance of 60 meters, the estimated allowance time period TY is 3.6 seconds (=(60/60000)xc3x973600). Accordingly, if the predetermined time period T is set to 4 seconds, a warning is given. However, if the relative speed is erroneously detected as 40 km/h at the distance of 60 meters, the estimated allowance time period TY becomes 5.4 seconds (=(60/40000)xc3x973600). Then a warning is not given although the probability that the collision may occur after 3.6 seconds is high. Even in this case, a warning is given after a little while, since the accuracy of detecting the distance becomes higher as the distance decreases. That is, the timing of giving a warning is delayed. In contrast, if the relative speed is erroneously detected as higher than the actual speed, the timing of giving a warning becomes too early.
Further, the above-described conventional method causes another problem that the vehicle running in the opposite lane and approaching at a comparatively high speed, or the vehicle running ahead in the same lane may be detected as an object with high possibility of collision, which often causes unnecessary warnings.
It is an object of the invention to provide a vehicle environment monitoring system, which is capable of more accurately determining the probability of collision between the object and the vehicle, thereby giving a waning to the driver at a desired timing, and preventing unnecessary warnings.
To attain the above object, the present invention provides a vehicle environment monitoring system, which detects an object existing in an external environment of the vehicle from an image, obtained by imaging means mounted on the automotive vehicle. The vehicle environment monitoring system includes vehicle speed detecting means, distance calculating means, relative speed calculating means, and probability determining means. The vehicle speed detecting means detects a running speed of the vehicle. The distance calculating means calculates a distance between the object and the vehicle, based on the image obtained by the imaging means. The relative speed calculating means calculates a relative speed between the object and the vehicle, according to the distance calculated by the distance calculating means. The probability determining means determines whether or not there is a substantial probability that the vehicle may collide with the object, based on the running speed of the vehicle and the distance calculated by the distance calculating means. A warning alarm is generated, provided on condition that the relative speed between the object and the vehicle is in the vicinity of the running speed of the vehicle.
According to this vehicle environment monitoring system, it is determined whether or not there is a significant probability that the vehicle may collide with the object, based on the running speed of the vehicle instead of the relative speed, and the distance between the vehicle and the object. This probability is determined on condition that the relative speed is in the vicinity of the running speed of the vehicle, in other word, the sensed object is moving at a relatively low speed, or standing still. Therefore, it is possible to issue a warning at a desired timing, even if the detection error of the relative speed is relatively large. Further, since the determination is carried out on condition that the relative speed is in the vicinity of the vehicle speed, it is possible to substantially prevent unnecessary warnings when the vehicle is approaching another vehicle that is running in the opposite lane, or running ahead in the same lane.
Preferably, the determining means carries out the determination, when an absolute value of a difference between the relative speed and the running speed of the vehicle is less than or equal to half of the running speed of the vehicle.
Preferably, the vehicle environment monitoring system further includes relative position-detecting means and movement vector-calculating means. The relative position-detecting means detects a relative position of the object to the vehicle, based on the image obtained by the imaging means and the distance calculated by the distance calculating means, to thereby obtain position data. The movement vector-calculating means calculates positions of the object in a real space, based on a plurality of time series items of the position data detected on the object by the relative position-detecting means, and calculates a movement vector of the object based on the positions in the real space. The probability determining means determines whether or not the probability of collision is high based on the movement vector, when it is determined based on the running speed of the vehicle and the distance that there is a possibility of collision.
According to this configuration, an accuracy of the determination is improved by using the movement vector.
Preferably, the movement vector-calculating means includes approximate straight line-calculating means for calculating an approximate straight line approximating a locus of relative movement of the object, and position data-correcting means for correcting the time series items of the position data by using the approximate straight line. The movement vector-calculating means calculates the movement vector based on the corrected time series items of the position data.
According to this configuration, a detection error relating to position data is reduced, to make it possible to more accurately determine the probability of collision.
Preferably, the probability determining means carries out the determination by applying collision determination conditions that are dependent on a width of the vehicle.
According to this configuration, the probability of collision is more accurately determined and unnecessarily alarms are prevented.
More preferably, the approximate straight line-calculating means calculates the approximate straight line as a three-dimensional straight line including data of a height of the object.
According to this configuration, it is possible to accurately determine the probability of collision, even when the vehicle is running on a hilly road.
Preferably, the imaging means comprises two infrared cameras capable of detecting infrared rays.
According to this configuration, an animal, a running automotive vehicle, or the like can easily be detected, even when the driver is driving at night and it is difficult to recognize them.
Preferably, the imaging means comprises two TV cameras for detecting infrared rays or visible rays, and the relative position-detecting means includes search area-setting means and corresponding object image-identifying means. The search area-setting means sets, based on a position of an object image contained in an image output from one of the two TV cameras, a search area within an image output from the other of the two TV cameras, for searching for a corresponding object image contained in the image output from the other TV camera. The corresponding object image-identifying means identifies the corresponding object image by carrying out a correlation operation on data within the search area. The distance-calculating means calculates the distance between the vehicle and the object, based on a parallax between the first object image and the corresponding object image.
Preferably, the vehicle environment monitoring system includes warning means for warning a driver, when it is determined by the determining means that there is a high probability of collision against the object. The warning means is preferably inhibited from warning the driver when the driver is carrying out a braking operation, and at the same time, deceleration caused by the braking operation is larger than a predetermined threshold.
According to this configuration, the driver is not warned when he has already recognized the object and is carrying out an appropriate braking operation. This makes it possible to substantially prevent the driver from being annoyed by an unnecessary warning.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.